Sunday, December 13, 2015

Storm system to bring snow to Red River valley and SE Manitoba Wednesday.. colder temperatures to follow

Mild weather continues over southern Manitoba with extensive cloud,
patchy fog and occasional freezing drizzle. This stagnant weather pattern is
expected to persist for the next couple of days before a more
significant storm tracking through Minnesota Wednesday impacts southern Manitoba
with snow and increasing winds. There remains some uncertainty with the track of this storm, which will influence snowfall amounts over southern Manitoba. At this point, models are indicating the heaviest snow with this system will fall mainly in eastern North Dakota and northern Minnesota, with lesser amounts over southern Manitoba. Even so, southeast Manitoba and the Red River valley should see some snow with this system, with 5-10 cm possible for most areas. Should the system track a bit further west, snowfall amounts will likely be higher across southern Manitoba. Note also that the system will be bringing increasing north winds Wednesday, which would lead to blowing and drifting snow issues especially over the Red River valley. Stay tuned for future updates on this developing system.

Average temperatures in Winnipeg overpast 90 days shows persistent warmth

A change to colder weather will follow in the wake of this system for the end of the week into the weekend, with temperatures falling to more seasonable levels for mid December. Keep in mind, normal highs are now -10C in southern Manitoba with lows of -20C.. temperatures we have yet to see so far this season. The coldest temperature since Nov 1st in Winnipeg has been only -17.5C on Nov 26th, and we've only dropped below the -15C mark on only 2 occasions so far this season. Truly remarkable given that normal lows are now -20C. Temperatures have been so consistently above normal over southern Manitoba over the past 2 months that dropping to near normal temperatures would seem like a bitter cold snap. Thanks to the strongest El Nino since 1997, Arctic air intrusions have been blocked from surging southward, allowing a persistent flow of mild Pacific air to prevail over the Prairies and much of north America. In the past 8 weeks, Winnipeg has seen only 5 days below normal, with none since Nov 27th. So a change to even normal temperatures will seem cold. However, indications are the cold weather will not be that intense or prolonged, with above normal temperatures expected to return by next week. This is consistent with a strong El Nino winter, where cold air intrusions are less frequent and shorter in duration.

9 comments:

Winter storm watch issued for North Dakota and northwest Minnesota.. generally south of a line from Devils Lake to Sprague MB. 10-20 cm of snow possible Tuesday night through Wednesday.

As for Winnipeg, looks like snow will be moving in here sometime Tuesday night, probably after midnight and continuing into Wednesday afternoon. We'll likely have at least 2-5 cm of new snow by Wednesday morning rush hour so plan for a slow commute into work or school Wednesday. Snow tapers off later in the afternoon with another 2-5 cm possible. Winds will be moderate out of the north but not strong.. so blowing and drifting snow should not be a big issue. All in all, a fairly tame snowstorm by Manitoba standards, but our first real snowfall to contend with since late November..

EC has issued a Special Weather Statement with general 5-10, but 10-20 CM possible is some areas. Rob, I notice you mention winds will not be too strong during entire system, does this still seem to be the case?

Winds look like they'll be picking up from the northwest later in the afternoon into the evening.. generally after the main dump of snow has fallen. But during the main snowfall, winds shouldn't be that strong which would cause more serious problems with blowing and drifting.

As far as 10-20 cm for southern MB, it's possible some areas may see those higher amounts, but it will be localized and not widespread. There are some hints that there may be a few hours of a locally heavier snowband setting up over the Red River valley in the morning, which would enhance amounts under that band. But in general, it's still looking like 5-10 cm for most areas. It's true that this is a system coming out of Colorado, but it's not one of this big bad Colorado lows that brings much stronger winds, heavier snow and blizzard conditions to southern MB.

Model guidance coming in tonight with slightly higher amounts for Winnipeg Wednesday.. now suggesting 10-15 cm thanks to a heavier burst in the morning. They show a dry slot pushing in over SE MB which would push the heavier snow amounts further west.. possibly over the western RRV where there would be some enhancement with NE upslope winds in the morning. So snowfall amounts could end up being heavier west of Winnipeg, less east of the city, and then heavier again over eastern ND and northern MN closer to storm system.

As you can see, complicated situation over southern MB with dry slot issues impacting where heavier snow totals will fall. Suffice to say, there will be a period of moderate to possibly heavy snow affecting Winnipeg and the RRV Wednesday morning before tapering off in the afternoon or evening. Northeast winds of 20 km/h in the morning will gradually shift to northwest 30 in the afternoon and evening. Traffic will be impacted, both morning and evening commutes.

As the graph shows, it's been an unusually warm start to the winter this year. We've only had 5 days below normal over the past 8 weeks. I only wish this was normal for Winnipeg, but clearly it's an anomalous year.

Models coming in line that heaviest swath of snow tomorrow will set up somewhere from the Pilot Mound-Altona area north through Winnipeg into southern Lake Winnipeg region. 10-20 cm possible within this swath. 10 cm outside this main area. Dry slot will give lesser amounts to our southeast and has pushed the heavier band further west.. which is why initial forecast of heavier amounts southeast of Winnipeg has changed.

Snow expected to move into Winnipeg between 3-6 am overnight, and become heavier by 8 am or so tomorrow with 2-5 cm of new snow by the morning rush hour. So expect a slower commute into work or school tomorrow morning. A period of moderate to heavy snow is expected through noon hour with another 5-10 cm by midday before snow eases off in the afternoon and evening with another 5 cm or so. Very slow commute for the drive home.. (unless everyone leaves earlier because of the storm) All in all.. 12-20 cm possible for Winnipeg by Wednesday night. Could see occasional light snow into Thursday morning with another couple cm possible. Winds will also pick up later tomorrow into tomorrow night so drifting and some blowing snow will become an issue although bulk of snow will be over by then.

That's what the latest guidance is saying.. now let's see how it all pans out. Got my snow ruler ready!